To create an external Slack channel, you need Slack Connect, a feature available on Slack’s paid plans (Pro, Business+, or Enterprise). Every organization participating in the channel must also be on a paid plan. Free-plan users can only send one-to-one external direct messages, not collaborate in shared channels.
What You Need Before Starting
Both your organization and the external organization you want to collaborate with need a paid Slack subscription. This is a hard requirement: if either side is on the free plan, the shared channel won’t work. A single Slack Connect channel can host up to 250 organizations, so you’re not limited to just one outside partner.
Your workspace admin also needs to have Slack Connect permissions enabled. If you try to send an invitation and the option isn’t available, it likely means your admin has restricted who can initiate external connections. On Pro and Business+ plans, Workspace Owners control these settings. On Enterprise plans, Org Owners and Org Admins manage them.
How to Create the Channel and Send Invitations
Start by creating a new channel the same way you’d create any Slack channel, or choose an existing one you want to open up to an outside organization. Give it a clear, descriptive name since people from multiple companies will be using it.
Once the channel exists, send an invitation to the people at the external organization you want to collaborate with. The recipient gets a notification and their admin may need to approve the connection before the channel goes live. Until both sides accept, the invitation stays in a pending state.
When you send the invitation, you’ll choose one of two permission levels for external members:
- Permission only to post: External members can send messages, use emoji reactions, add files, and use workflows. They cannot add other people, install apps, rename the channel, or change its privacy settings.
- Permission to post, invite, and more: External members get full collaboration rights, including the ability to invite others from organizations already in the channel, add apps and workflows, change the channel name or topic, and convert the channel between public and private within their own workspace.
The “post only” option is the safer default when working with vendors or short-term partners. The fuller permission set works better for tight collaborations where the external team needs to help manage the channel.
Admin Settings That Control Invitations
If you’re a Workspace Owner on a Pro or Business+ plan, you can configure who’s allowed to send external invitations:
- Click Admin in the sidebar, then select Workspace settings.
- Go to the Permissions tab.
- Expand Slack Connect Channels.
- Toggle permissions on or off for each invitation type, then choose which members can send them.
- Click Save.
On Enterprise plans, the path is slightly different: click your organization name in the sidebar, go to Tools & settings, then Organization settings. From there, navigate to Slack Connect in the left sidebar, select Settings, then the Channels tab. You’ll find the same toggles for invitation types and who can send them.
Enterprise admins have an additional option to restrict Slack Connect channels to specific workspaces only, which is useful for large organizations that want to limit external collaboration to certain teams.
Why Invitations Get Stuck
The most common reason an invitation stays pending is that the other organization’s admin hasn’t approved it yet. Many companies require administrative approval before any external channel connection goes live, especially in regulated industries or large enterprises.
Other reasons invitations stall:
- The external organization is on Slack’s free plan and can’t join shared channels.
- Your admin has turned off the ability for your role to send Slack Connect invitations.
- The receiving organization has custom approval workflows that route requests to a specific team before they’re accepted.
Admins can speed things up by configuring automatic acceptance for trusted partner organizations. On Pro and Business+ plans, go to Directories, then External, then Manage connections. Click the three-dot menu next to the organization and select Edit acceptance settings. Enterprise plans have a similar option under Organization settings in the Slack Connect section. You can also set up automated approval rules using Slack Connect APIs on Enterprise plans, which lets you pre-approve invitations that meet certain criteria and block ones that violate your guidelines.
Managing External Members After Setup
Once the channel is live, each organization retains control over its own members and data. If you chose the “permission only to post” level, external members can participate in conversations but can’t make structural changes to the channel. You can adjust these permissions later if the relationship evolves.
Org Owners and Admins can also control who external members are allowed to invite into channels. This prevents a situation where a partner organization adds a third party you didn’t expect. You’ll find this setting under Organization settings, then Slack Connect, then Settings, under the Channels tab next to “External people can invite.”
If a partnership ends, you can remove an organization from the channel entirely. Their members lose access, though organizations with full permissions will retain an archived copy of the channel on their side.